This invention relates generally to optical metrology methods and apparatus and, more particularly, to those systems employing light sources that generate optical signals that are difficult to transmit over fiber optics, such as ultrafast, UV and/or high power or low light level optical signals, and relates as well to optical metrology systems that generate short pulses of laser energy for application to a surface of a sample, such as a surface of a silicon wafer.
The increasing sophistication of semiconductor technology has resulted in a significant increase in the sophistication of the process equipment designed to produce the films used to manufacture semiconductor integrated circuits. One strategy to improve the performance of film deposition systems is to incorporate metrology into the process tools. The limitations of packaging size, as well as system cost and performance, are critical to the success of this application.
A first problem that remains to be solved is how to reduce the cost and size of metrology systems, particularly systems for integrated or insitu metrology. Presently, conventional metrology systems are self-contained and include all of the optical components required to make a measurement. Although some designs offer selected electronics or remote components to improve packaging, no cost sharing can be done across components. For integrated metrology it is important to offer capable metrology at an affordable value. What is needed is a technique to dramatically reduce the cost of metrology components.
A second problem that remains to be solved is how to reduce the cost and size of metrology without reducing the performance of the metrology. The best available technique for reducing the cost and size of metrology is to reduce the cost of the components and/or reduce the capability. One known type of system that takes this approach results in a capability embodied as a simple reflectometer. Although the reflectometer meets the cost and packaging goals of an integrated system, the capability and performance are limited. What is needed is an effective technique to bring complex and highly capable metrology to cost-effective integrated systems. Relatedly, in addition to reducing the cost there is a need to increase the reliability of the components.
A third problem that remains to be solved is how to increase the reliability of the system. Since reliability and availability are limited by component lifetimes and Mean Time Between Failure (MTBF) considerations, one technique to improve reliability is to provide redundant components. However, since the components that need to be made redundant may also be expensive, there may be a prohibitive cost penalty for providing redundancy in components such as lasers. What is needed is a technique to provide redundancy for high cost components without enduring an increase in the cost to the system.
A fourth problem that remains to be solved is how to deliver optical beams that are not well transmitted by fiber optics, such as ultrafast signals, to a remote metrology system. Current systems typically package an ultrafast laser with the metrology system because of the difficulty of transferring ultrafast signals. What is needed is a technique to transfer ultrafast signals, particularly with a metrology capability encoded in the signal, to a remote metrology system.
A fifth problem that remains to be solved is how to provide multiple different metrology capabilities in an inexpensive, integrated metrology system. Current systems must add different metrology capabilities (i.e. measurement systems) to the same package to deliver increasing measurement and diagnostic capabilities. What is needed is an ability to provide different metrology capabilities in a single, core metrology system.
A further problem that remains to be solved is how to provide for a mixed set of integrated and off-line metrologies at a reduced cost. Current metrology systems may combine multiple metrology capabilities by adding all of the components to one package. However, some of these components may be xe2x80x98idlingxe2x80x99 for a substantial portion of the time since not all measurements are required at the same time. This idling of metrology components increases the cost of ownership of the metrology system since components have been paid for but are not being used. In some cases, valuable consumables may be expended while components are idling. What is needed is a method to make multiple metrology measurements available without incurring the increased cost and depreciation of the individual components.
Another problem that remains to be solved is how to provide metrology on demand. Some metrologies are needed only occasionally. Since the need is only occasional, it is wasteful to have all of the metrological capabilities available at all tools at all times. What is needed is a way to have different metrologies available as they are required by the user, without incurring the cost on a per-system basis.
Another problem that remains to be solved is how to improve the maintainability of a metrology system. Since space in a wafer fabrication facility (fab) is very expensive, metrology system designs are typically created that minimize the size in the fab. The most critical size component to reduce is the xe2x80x98bay frontagexe2x80x99, i.e,. the width of the unit to the operator. This demand on space may force compromises to be made in the maintainability of a tool. However, space behind the unit is more readily available. What is needed is a system in which most of the components of a metrology system can be placed in a location where floor-space is not so valuable such that more space can be devoted to facilitate maintenance access.
It is a first object and advantage of this invention to provide an improved metrology system that solves the foregoing and other problems.
It is a further object and advantage of this invention to provide an optical metrology system wherein one or more laser servers are employed to deliver pulses of laser energy to a plurality of metrology stations or heads, also referred to as metrology slaves, through a laser energy delivery system, such as optical fiber or a light pipe or conduit.
The foregoing and other problems are overcome and the foregoing objects and advantages are realized by methods and apparatus in accordance with embodiments of this invention.
This invention provides a system having one or more central xe2x80x98metrology serversxe2x80x99 and one or more xe2x80x98metrology slavesxe2x80x99. The metrology server delivers metrology xe2x80x98probexe2x80x99 signals to multiple slave systems allowing a reduction in the number of high-cost metrology components in the master system. In certain cases, multiple metrology components in the xe2x80x98masterxe2x80x99 system may provide redundancy while still maintaining a beneficial cost benefit.
Economies of scale apply to the laser design since the efficiency of many of the laser processes are improved with increasing laser power. For example, frequency doubling efficiency improves as does the opportunity for continuum generation, such as providing white light from the laser for spectroscopic work. There is also a potential for recovering the discarded pump modulation (15%-30% of laser power recovery) when multiple systems are run from one laser.
Reliability can also be improved by using multiple lasers and multiple delay paths with a cross-point switch between them. If one sub-system goes down, the system may xe2x80x98serializexe2x80x99 metrology operations and thereby maintain all systems operational, although at somewhat of a reduced throughput.
An important element of this invention is grouping all or most of the costly components in a centralized laser server, and issuing pump-probe pulse pairs to remote metrology heads. The remote metrology heads can be reduced in cost and complexity.
A first aspect of the present invention is a method for reducing the cost and size of an integrated metrology system by sharing the output of high cost components between multiple measurement modules by transmitting the generated light signals between multiple systems.
A second aspect of the invention is a technique for reducing the cost and size of the integrated metrology systems by time-sharing the source of the metrology signals between multiple systems.
A third aspect of the invention is using an excluded beam from a modulator in an apparatus to serve as the modulated signal for a second shared apparatus.
A fourth aspect of the invention is using multiple different master systems to feed multiple slaves designed to use the different signals to make different types of measurements.
A fifth aspect of the invention is using multiple redundant components in the xe2x80x98masterxe2x80x99 system to improve the reliability, along with a cross-point switching or similar network to engage alternate sources upon one failed component.